Schizophrenia, Alzheimer's Disease, autism, depression, benign forgetfulness, childhood learning disorders, close head injury, and attention deficit disorder are examples of neuropsychiatric disorders. Autism, for example, is a developmental mental disorder characterized by autistic behavior, social failure, and language delay. Alzheimer's Disease is a form of dementia that typically involves progressive mental deterioration, manifested by memory loss, confusion, and disorientation. Alzheimer's Disease typically is treated by acetylcholine esterase inhibitors such as tacrine hydrochloride or donepezil. Attention Deficit Disorder is a disorder that is most prevalent in children and is associated with increased motor activity and a decreased attention span. Attention Deficit Disorder commonly is treated by administration of psychostimulants such as Ritalin or Dexedrin. Depression is a clinical syndrome that includes a persistent sad mood or loss of interest in activities, which persists for at least two weeks in the absence of treatment. Conventional therapeutics include serotonin uptake inhibitors (e.g., PROZAC.TM.), monoamine oxidase inhibitors, and tricyclic antidepressants.
The term schizophrenia represents a group of neuropsychiatric disorders characterized by dysfunctions of the thinking process, such as delusions, hallucinations, and extensive withdrawal of the patient's interests from other people. Approximately one percent of the worldwide population is afflicted with schizophrenia, and this disorder is accompanied by high morbidity and mortality rates.
Conventional antipsychotic drugs, which act on the dopamine D.sub.2 receptor, can be used to treat the positive symptoms of schizophrenia, such as delusion and hallucination. In general, conventional antipsychotic drugs and the new atypical antipsychotic drugs, which act on the dopamine D.sub.2 and 5HT.sub.2 serotonin receptor, are limited in their ability to treat cognitive deficits and negative symptoms such as affect blunting (i.e., lack of facial expressions), anergia, and social withdrawal.